Process for preparing a viscose solution



PROCESS FGR PREPARING A VECOSE SULUTION John L. Justice, Wallingford, Pa., assignor to American Viscose Corporation, Philadelphia, Pa, a corporation of Delaware No Drawing. Application January 21, 1953, Serial No. 332,577

8 Claims. (Cl. 260-213) This invention relates generally to a process for producing viscose having improved properties, and in particular relates to the formation of modified regenerated viscose.

It has been shown in U. S. Patent 2,524,399 issued October 3, 1950, to Dwight L. Schoene and Victor S. Chambers that fabrics and yarns, including continuous filament yarn and staple fiber yarn, composed of cellulose or cellulose derivatives may be produced that are dimensionally stable to water by reacting the cellulosic textile with divinyl sulfone in the presence of a basic catalyst. According to this patent from 0.1 per cent to 100 per cent, based on the weight of the cellulose, of divinyl sulfone may be reacted with the textile. It is pointed out, however, that with increasing concentration progressive decrease in the tensile strength results. The

eneral procedure suggested for applying the divinyl sulfone to the textile is by impregnating the textile with an aqueous solution of the divinyl sulfone, removing the excess solution, immersing the textile in an alkaline bath, again removing the excess solution, allowing the fabric to stand for a period of time to allow the reaction to take place and then removing the excess divinyl sulfone and drying the fabric. The steps can be varied by treating with the alkali before or concurrently with the sulfone, and the reaction may be carried out at any temperature from C. to 100 C. The treated textile is dimensionally stable to water and insoluble in the usual solvents for cellulose, such as cupraammonium and the quaternary ammonium hydroxides.

it has now been discovered that an article having dimensional stability to water and one that also has substantial uniformity throughout, solubility in the usual cellulose solvents and increased tensile strength, may be produced by reacting alkali cellulose with divinyl sulfone, xanthating the reaction product, dissolving the xanthate in alkali and subsequently forming the solution into shaped articles, such as filaments, fibers, yarns, films, rods, etc. This is distinct from the prior practice where the regenerated cellulose fiber or fabric was treated with divinyl sulfone and also results in a product having properties that are distinct from what would be expected from the prior art.

According to the present process after the treatment of alkali cellulose with divinyl sulfone and xanthation thereof, the product is soluble in caustic soda solutions and may be spun into a yarn or other article that has both increased tensile strength and dimensional stability to water. These properties are attributed to the fact that by treating the alkali cellulose with the divinyl sulfone a much more uniform reaction between the cellulose and the sulfone is obtained. This is believed to be due in part to the fact that the reactants may be more readily controlled and more uniformly mixed, whereas when fabric or yarn is treated the reaction occurs primarily at the surface.

The present process involves an additional step in the Zflhdfiild Patented .luly 3, M356 viscose process. The viscose process in general involves the chemical treatment of cellulose to a point where it is in such condition that when extruded into a suitable coagulating bath it will result in a product having desirable physical properties. The viscose process in general proceeds as follows: Cellulose pulp in the form of sheets is soaked in a caustic soda solution to convert the cellulose to alkali cellulose. When the conversion has taken place the excess caustic solution is removed and the sheets are placed in a shredder. The shredded sheets are called alkali cellulose crumbs. The crumbs are then aged and subsequently treated with carbon disulfide to convert the alkali cellulose into cellulose xanthate. The step of treating the alkali cellulose with carbon disulfide is called xanthation. After xanthation the crumbs are dissolved in a solvent such as a caustic soda solution to produce viscose and aged until the solution reaches the proper viscosity. it is then pumped through a spinneret or suitable forming device into a coagulating bath which coagulates the solution. If the article formed is yarn it is then stretched to increase the tensile strength and further processed to remove the by-product impurities.

The additional step which is added to the viscose process according to this invention is the reacting of the alkali cellulose with divinyl sulfone before xanthation. This reaction may be carried out at any temperature, but the preferred temperature is approximately 16 to 20 C., since it is desirable to maintain the alkali cellulose in this temperature range. he divinyl sulfone may be dis solved in a solvent so that the small amount of sulfone used is uniformly distributed throughout the alkali cellulose. Any solvent that does not react with the alkali cellulose or the divinyl sulfone is suitable, such as tetrahydrofuran, ethyl ether, benzene, chloroform, and dioxane. The time required for the reaction will vary with the conditions, but the preferred time is from 30 to minutes. As a general rule the time varies inversely to the temperature.

it is unnecessary in this treatment to add a basic catalyst to the reaction mixture since the alkali cellulose coni tains a certain amount of alkali. The reaction rate will be determined in part by the strength of the alkali presout. By varying the amount of caustic in the alkali cellulose, within workable limits, the rate of reaction may be controlled.

A preferred procedure for carrying out the additional step in the viscose process is to react the alkali cellulose crumbs with divinyl sulfone dissolved in tetrahydrofuran. After the divinyl sulfone has reacted with the alkali cellulose crumbs the solvent is removed. The crumbs are then xanthated by treating with carbon disulfide. The amount of divinyl sulfone allowed to react with the alkali cellulose has to be kept within rigid limits. If too great an amount of divinyl sulfone is reacted with the alkali cellulose crumbs, the resulting xanthate after treatment with carbon disulfide will be insoluble in aqueous alkali and, therefore, not capable of being spun into fibers. The amount of divinyl sulfone that may be reacted with the alkali cellulose while maintaining the desired solubility is generally in the range of from 0.05 to 0.5 per cent by weight, based on the weight of the alkali cellulose.

The following examples are intended to be illustrative of the invention.

Examples The alkali cellulose crumbs were prepared in accordance with the viscose process by the steeping of cellulose sheets with 18 per cent caustic soda, removing the excess caustic until the sheets are only about three times the weight of the dry sheets and then shredding the sheets,

The crumbs were aged at 18 C. for 72 hours and then treated with a solution of divinyl sulfone in tetrahydrofuran in amounts specified in the accompanying table. The crumbs were allowed to soak in the solution for one hour at 18 C. with constant agitation. The crumbs were then separated from the solution and xanthated. The xanthate was further treated according to the viscose process by dissolving in a sodium hydroxide solution. The solution containing the dissolved xanthate had a composition of approximately 7.5 per cent cellulose, 7.8 per cent sodium hydroxide, 2.2 per cent sulfur and the remainder water. The solution was aged until it had a salt index of from about 2 to 7 and then formed into yarn by extruding into a coagulating bath composed of 10 per cent sulfuric acid, 22 per cent sodium sulfate, 4.5 per cent zinc sulfate, per cent glucose and the remainder water. The yarn was stretched immediately upon leaving the bath. This procedure was used in all of the examples shown in the table.

4. cellulose, of divinyl sulfone, xanthating the reaction prodnot, and dissolving the xanthated product in a caustic soda solution.

2. Process for preparing a viscose solution comprising 5 the steps of reacting alkali cellulose crumbs with .05.5%

by weight, based on the weight of the alkali cellulose, of divinyl sulfone, xanthating the reaction product, dissolving the xanthated product in a caustic soda solution, and ageing it therein to a viscosity suitable for subsequent spinning and casting.

4. Process of claim 3 wherein the solvent is tetrahydrofuran.

5. Process of claim 3 wherein the solvent is ethyl ether. 6. Process of claim 3 wherein the solvent is benzene.

7. Process of claim 3 wherein the solvent is chloroform.

. 1. M1. of Tenacity, Extensibility, D VS /600 Tetra- Percent Denier/ grams/denier Percent Examples g, of hydro- Stretch Fila- Alkali furan ments Cellulose Dry Wet Dry Wet 1 Divinyl sulfone.

The invention has been described with respect to the forming of filaments or yarns, but it is equally eflective in forming other articles, such as films, rods or the like.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not limited to the details described herein, except as set forth in the appended claims.

I claim:

1. Process for preparing a viscose solution comprising the steps of reaction alkali cellulose crumbs with .05.5% by Weight, based on the weight of the alkali 8. Process of claim 3 wherein the solvent is dioxane.

35 References Cited in the file of this patent UNITED STATES PATENTS 1,952,604 Parker Mar. 27, 1934 2,069,774 Reid Feb. 9, 1937 2,302,589 Rose Nov. 17, 1942 2,524,399 Schoene et al. Oct. 3, 1950 2,539,704 Schoene et al. Jan. 30, 1951 FOREIGN PATENTS 365,982 Great Britain Jan. 28, 1932 155,737 Switzerland July 15, 1932 

1. PROCESS FOR PREPARING A VISCOSE SOLUTION COMPRISING THE STEPS OF REACTION ALKALI CELLULOSE CRUMBS WITH .05-% BY WEIGHT, BASED ON THE WEIGHT OF THE ALKALI .05-.5% CELLULOSE, OF DIVINYL SULFONE, XANTHATING THE REACTION PRODUCT, AND DISSOLVING THE XANTHATED PRODUCT IN A CAUSTIC SODA SOLUTION. 